Glass core guidewire compatible with magnetic resonance

ABSTRACT

A guidewire compatible for use with magnetic resonance systems is made from a non-metallic material with a high specific electric impedance, preferably constructed primarily of a glass body. Possible material selections for the glass body include quartz. Further enhancements to the present invention are as follows. Moreover, the glass body may be sheathed in a protective polymer layer, which is also non-metallic and tends to improve the physical characteristics of the guidewire. The sheath may preferably be reinforced with a number of reinforcing fibers, which may be made from carbon, borium, aramide and also various types of glass fibers. If necessary to obtain the desired physical performance of the guidewire, including high flexibility at the distal end, a distal portion of the guidewire may be constructed of metal components according to designs known in the art. Such a metal tip portion may be made of nitinol, and should be substantially shorter than the wavelength of the magnetic resonance field.

BACKGROUND AND SUMMARY OF THE INVENTION

1. Technical Background:

The present invention relates generally to intravascular medicaldevices, and more particularly, to a medical guidewire for use withmagnetic resonance systems. Such guidewires may be used in medicalprocedures for both diagnostic and interventional purposes.

2. Discussion:

Guidewires are used in a wide variety of medical procedures, most oftenin conjunction with one or more other medical devices, includingcatheters. Such a catheter may be any of various types, such asangiography or angioplasty, but should in any event have a tubular lumenor other guiding means through which the guidewire can be advanced orwithdrawn.

Structurally, guidewires are often long, thin metal wires that generallytaper from one diameter at a proximal end which remains outside the bodyof the patient, to a smaller diameter at the opposite distal end.Specifically, vascular guidewires are often more than five feet long andhave a maximum outer diameter of approximately 0.038 inches. Thediameter of the core wire is generally ground down precisely in a seriesof alternating tapering portions and constant diameter sections, todevelop a selectively engineered flexibility profile along the length ofthe guidewire.

The guidewire distal tip is usually very flexible, both to avoidvascular trauma and so that it can be selectively bent and twisted toadvance it along a desired vascular path. Guidewires a redesigned toresist this twisting force or torsion, so that as the guidewire proximalend is twisted or rotated, the distal tip tends to rotate through aboutthe same angle. In addition, a floppy spring is often affixed to theextreme distal tip of the guidewire for flexibility.

A good example of a current guidewire is described in the commonlyassigned U.S. Pat. No. 4,846,186, issued to Box et al. on Jul. 11, 1989,which is incorporated in this disclosure by reference. The Box patentshows a guidewire suitable for both diagnostic and therapeutic orinterventional procedures, having a Teflon coating from the proximal endalong a majority of its length. The core wire tapers in steps to adistal portion that is flattened and surrounded by a flexible spring,which is brazed to the extreme distal end of the core wire to form arounded tip.

As the body of the patient is of course opaque, physicians commonly usefluoroscopy or X-ray video cameras to track the position of theguidewire and to construct real-time images of the patient'svasculature. The visibility and brightness of selected portions of theguidewire is a relatively important feature, as described in thecommonly assigned U.S. Pat. No. 5,259,393, issued to Corso, Jr. et al.on Nov. 9, 1993, and U.S. Pat. No. 5,267,574, issued to Viera et al. onDec. 7, 1993. Both of these patents are incorporated in this disclosureby reference. In the Corso patent, the flexible spring at the guidewiredistal tip is arranged to selectively control its brightness on an X-rayfluoroscope, or radiopacity. Likewise, the Viera patent discloses aplastic sleeve shrunk around an intermediate section of the guidewire,and several radiopaque marker bands.

In contrast to fluoroscopy, another method of visualizing the patient ismagnetic resonance imaging, referred to as MRI. Other medical fields,such as neurology, often use procedures which are performed under MRIinstead of X-ray fluoroscopy. Accordingly, it is also desirable to imagethe anatomy and to track the position of intravascular devices,including catheters and guidewires, using magnetic resonance (MR)systems.

For these applications, it is desirable to make guidewires usable andcompatible with MRI techniques. However, a metal guidewire may be toovisible under MR, brightly washing out the screen and obscuringimportant features. This halo phenomenon is called an “artifact,” andrenders the image useless. Another issue with the use of a metalguidewire under MR is the induction of eddy currents in the metal,caused by distortion of the magnetic field. These eddy currents cangenerate heat and may increase the local temperature of the surroundingtissue and body fluids, thus possibly damaging the tissue or causing theblood to coagulate.

It is an object of the present invention to provide a guidewire havingthe desired physical features, including torsion and flexibility, whilealso avoiding the creation of undesirable artifacts in the MR image orthe generation of heat.

The present invention provides a guidewire compatible for use withmagnetic resonance systems, made from a non-metallic material with ahigh specific electric, impedance. Accordingly, this material willresist any electrical eddy currents in the guidewire from beinggenerated by variations in the high-frequency field. An acceptable classof materials is glass, which are all electrical insulators. A guidewirehaving a major portion constructed of a glass material should thereforehave the advantages of not disturbing the MR field and images, as wellas resisting the generation of heat.

These and various other objects, advantages and features of theinvention will become apparent from the following description andclaims, when considered in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a guidewire for use with magneticresonance systems, arranged according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of a portion of the guidewire of FIG.1, in a location near that indicated by arrow II;

FIG. 3 is a cross-sectional view of a portion of the guidewire of FIG.1, in a location near that indicated by arrow III;

FIG. 4 is a perspective view of a guidewire for use with magneticresonance systems, arranged according to another embodiment of thepresent invention;

FIGS. 5-7 are cross-sectional views of a portion of various guidewiresarranged according to certain embodiments of the present invention;

FIG. 8 is a perspective view of a guidewire for use with magneticresonance systems, arranged according to another embodiment of thepresent invention;

FIG. 9 is a cross-sectional view of a portion of the guidewire of FIG.8, in a location near that indicated by arrow IX;

FIG. 10 is a cross-sectional view of a portion of the guidewire of FIG.8, in a location near that indicated by arrow X; and

FIGS. 11-13 are side elevation views of distal portions of guidewiresarranged according to alternative embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiments of the presentinvention is merely illustrative in nature, and as such it does notlimit in any way the present invention, its application, or uses.Numerous modifications may be made by those skilled in the art withoutdeparting from the true spirit and scope of the invention.

Referring to FIG. 1, a perspective view of a guidewire according to afirst preferred embodiment of the present invention is shown generallyat 1. The medical guidewire 1 is intended for use in intravascularmedical procedures involving the use of magnetic resonance systems,including both magnetic resonance imaging and magnetic resonancetracking of the guidewire's position within the body of the patient.Guidewire 1 is constructed of a basic body 2 and a distal tip portion 3.The distal tip of guidewire 1 includes several markers 4 embedded in thedistal tip portion 3, which are more visible under MR than the remainderof the guidewire.

The proximal portion of the basic body 2 is illustrated in FIG. 3, andincorporates a relatively long, thin core or glass body 5, which may beencased with a protective coating or cladding 6 for improving the breakstrength of the glass body 5. The cladded glass body 5 extends forsubstantially the length of the guidewire and is surrounded with apolymer sheath 7, which is adhered to the glass body 5 with a glue 8.

Markers 4 are visible under MR because their magnetic susceptibilitydiffers to a controlled extent from the remainder of the guidewire andsurrounding body tissue, thus distorting the uniformity of the magneticresonance field and causing the magnetic field to become what is called“locally inhomogeneous.” The material of the markers 4 is selectedspecifically for this property, and acceptable materials includeDysprosium Oxide (Dy₂O₃).

The glass body 5 is preferably made of a glass material having a highspecific electric impedance, such as fiberglass, silica, or quartz.

The cladding 6 adds strength to the glass core 5, in that the coatingallows the glass core 5 to be bent through a sharper turn or moretortuous path without breaking. Indeed, it has been found that thecladded glass core 5 may endure strain as high as 12%. A suitablematerial for the coating 6 has been found to be polyimide.

The outer polymer sheath 7 may be constructed from any of a variety ofmaterials, including nylon. An additional advantage of the design of thepresent invention is that the polymer sheath 7 can maintain the physicalintegrity of the guidewire, even if the glass core 5 should unexpectedlybreak. Of course, the polymer sheath 7 may be provided with a lubriciousor hydrophilic coating, as generally known in the art.

An intermediate portion of the guidewire is depicted in FIG. 2, whichfocuses on a region near the transition at arrow II between the glasscore proximal portion of the basic body, referred to as the “transitionpoint.”

The distal tip portion 3 of the guidewire 1 may be formed of a glass orplastic, as shown in FIG. 2, or of a metal as shown in FIGS. 8-13. Theouter diameter of guidewire 1 preferably tapers to a smaller diametertoward the distal tip, as illustrated in FIGS. 8-13. The metal tipportion may be a material having a selected magnetic susceptibility,such as stainless steel, nickel titanium (nitinol), or tantalum.Preferably, the length of the metal distal tip segment is substantiallyshorter than the wavelength of the magnetic resonance field in which theguidewire is used.

The glue 8 is preferably of a type that cures upon exposure toultraviolet light. Accordingly, the polymer sheath 7 should betransparent, to allow the glue 8 to be exposed to the ultraviolet lightafter portions of the guidewire I are assembled as shown in FIGS. 1-3.

An alternative embodiment of the present invention is depicted in FIGS.4-7, in which a guidewire 11 has a proximal portion 12 and a distal tipportion 13. Guidewire 11 has a plastic sheath 16 in which a number ofreinforcing fibers have been embedded. Sheath 16 may be shrunk around abundle of fibers 17, or the sheath 16 may be braided with thereinforcing fibers. Alternatively, fibers 18 may be embedded in apolymer matrix 19 In addition, a multiplicity of short reinforcingfibers 20 can be provided in a polymer matrix 21, surrounded by acoating 12. The reinforcing fibers may be of any suitable material, suchas carbon, borium, aramide, or glass.

The guidewire of the present invention may also be constructed of morethan one glass core body, all of which may be clad as a unit with asingle protective coating.

It should be understood that an unlimited number of configurations forthe present invention can be realized. The foregoing discussiondescribes merely exemplary embodiments illustrating the principles ofthe present invention, the scope of which is recited in the followingclaims. Those skilled in the art will readily recognize from thedescription, claims, and drawings that numerous changes andmodifications can be made without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A medical guidewire having a length greater than24 inches for use in intravascular medical procedures and compatiblewith magnetic resonance, the guidewire having proximal and distal ends,comprising: at least one thin core fiber extending for substantially thelength of the guidewire, the core fiber being made of a glass having ahigh specific electric impedance; wherein a distal segment of the glasscore fiber tapers to a diameter at its distal end that is smaller thanthe diameter of a major portion of the core fiber; a polymer sheathsurrounding the core fiber, and which is affixed to the core fiber atleast at a proximal and a distal end with an adhesive; wherein the corefiber has a breaking strength, said core fiber being covered with acladding for increasing said breaking strength and; at least one markerpositioned near a distal end of the guidewire, wherein the marker isvisible under magnetic resonance due to susceptibility-induced magneticfield inhomogeneity, and wherein the guidewire is formed substantiallyentirely of non-metallic materials.
 2. The medical guidewire of claim 1,further comprising a plurality of reinforcing fibers affixed to the coreto enhance the flexibility and torsion characteristics of the guidewire.3. The medical guidewire of claim 1, further comprising a plurality ofreinforcing fibers affixed to the polymer sheath to enhance theflexibility and torsion characteristics of the guidewire.
 4. The medicalguidewire of claim 3, wherein the material of the reinforcing fibers isselected from the group consisting of carbon, borium, aramide, andglass.
 5. The medical guidewire of claim 1, wherein the material of thecore is selected from the group consisting of fiberglass, silica, andquartz.
 6. The medical guidewire of claim 1, wherein the material of themarker Dysprosium Oxide (Dy₂O₃).
 7. The medical guidewire of claim 1,wherein the distal tip of the guidewire is bent slightly, to facilitatethe selective steering of the guidewire along a desired vascular path.8. The medical guidewire of claim 1, wherein at least a portion of thepolymer sheath has a hydrophilic coating.
 9. The medical guidewire ofclaim 1, wherein the core is formed of a plurality of glass corestrands.
 10. A medical guidewire having a length greater than 24 inchesfor use in intravascular medical procedures and compatible with magneticresonance, the guidewire having proximal and distal ends, comprising: athin core extending for substantially the length of the guidewire, thecore being made of a glass having a high specific electric impedance; apolymer sheath surrounding the core; at least one marker positioned neara distal end of the guidwire, wherein the marker is visible undermagnetic resonance due to susceptibility-induced magnetic fieldinhomogeneity; and a distal tip segment made substantially entirely ofmetal components affixed to the glass core at a transition point,wherein a length of the relatively short distal tip segment is shorterthan a wavelength of a magnetic resonance field in which the guidewireis used; wherein a remainder of the guidewire other than the distal tipsegment is formed substantially entirely of non-metallic materials. 11.The medical guidewire of claim 10, wherein the material of the metaldistal tip segment is nitinol.
 12. The medical guidewire of claim 10,wherein a distal segment of the glass core tapers to a diameter that issmaller than the diameter of a major portion of the core.
 13. Themedical guidewire of claim 10, wherein the polymer sheath extendscontinuously from a location near the proximal end of the guidewire, toa location distal of the transition point, thus surrounding at least aportion of both the glass core and the metal distal tip segment.
 14. Themedical guidewire of claim 10 further comprising a short metal collaraffixed to the guidewire at the transition point, to resist kinking andbreakage of the guidewire at the transition point.
 15. The medicalguidewire of claim 10 wherein the core has a breaking strength, saidcore being covered with a cladding for increasing said breakingstrength.